It is customary, in electrophotographic printers or copiers, to fix the recording medium, coated with toner, in a thermal fixing station. Thermal fixing stations of this type generally contain electrically heated fixing rollers having associated swing-to and swing-away pressure rollers. For the fixing, the recording medium is guided through between the fixing rollers and pressure rollers. The toner on the recording medium is fixed by the action of heat from the fixing roller. Since the toner has to be brought to melting temperature in the course of the short zone of contact of the recording medium with the fixing roller, a high heating capacity is necessary for the fixing roller. It is conventional, for this purpose, to install halogen radiators of high heating capacity in the hollow fixing roller.
But the disadvantage of halogen radiators is that their burning time is relatively short and that it is therefore necessary to exchange them quite frequently.
U.S. Pat. No. 4,493,982 makes known a device for extracting radiant heaters from the fixing station of a copier, which makes it possible to extract the radiant heater even in the hot state. The fixing roller remains in the housing of the machine.
European reference 0,184,202 (corresponding to U.S. Pat. No. 4,736,226) describes a fixing device having a fixing roller which is mounted on heating bars as bearing elements. To exchange the fixing roller, the heating bars are drawn out of the machine housing. An exchange of the fixing roller in the hot state is possible only with difficulty and only by a maintenance technician.
It has hitherto been customary, in the event of damage, for the exchange of the defective radiant heater and the defective fixing roller to be carried out by a trained maintenance technician, with the machine cold. This leads to a long machine shutdown and high expenditure for the repair of the machine. A particular disadvantage has been that, before the actual exchange, it has been necessary to wait until both the fixing roller and the halogen radiator to be exchanged have cooled. In view of the high thermal capacity of the fixing roller, this can take a relatively long time.
Moreover, to exchange the radiant heaters, it has been necessary to dismount the entire heating roller, thus additionally complicating the exchange.
Since the recording medium is moved between the fixing roller and pressure roller by means of friction, the pressure roller is subjected to relatively high wear. To exchange the pressure roller, it has hitherto been conventional to dismantle the entire fixing station. This involves a high outlay and leads to lengthy undesirable idle times of the printing apparatus.